.\" Copyright (c) 1994 SigmaSoft, Th. Lockert
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by SigmaSoft, Th. Lockert.
.\" 4. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" $OpenBSD: arch.1,v 1.2 1996/06/29 20:29:34 tholo Exp $
.\"
.\" Modifications made 8/20/97 (c) Apple Computer, Inc.
.\" Modifications made 11/12/06 (c) Apple Computer, Inc.
.Dd November 12, 2006
.Dt ARCH 1
.Os "Mac OS X"
.Sh NAME
.Nm arch
.Nd print architecture type or run selected architecture of a universal binary
.Sh SYNOPSIS
.Nm arch
.Nm arch
.Op Fl h
.Oo
.Oo Fl Ns Ar arch_name | Fl arch Ar arch_name Oc Ns ...
.Oc
.Ar prog
.Op Ar args No ...
.Sh DESCRIPTION
The
.Nm arch
command with no arguments, displays the machine's architecture type.
.Pp
The other use of the
.Nm arch
command it to run a selected architecture of a universal binary.
A universal binary contains code that can run on different architectures.
By default, the operating system will select the architecture that most closely
matches the processor type.
This means that an intel architecture is selected on intel processors and a
powerpc architecture is selected on powerpc processors.
A 64-bit architecuture is preferred over a 32-bit architecture on a 64-bit
processor, while only 32-bit architectures can run on a 32-bit processor.
.Pp
When the most natural architecture is unavailable, the operating system will
try to pick another architecture.
On 64-bit processors, a 32-bit architecture is tried.
If this is also unavailable, the operating system on an intel processor will
try running a 32-bit powerpc architecture.
Otherwise, no architecture is run, and an error results.
.Pp
The
.Nm arch
command can be use to alter the operating system's normal selection order.
The most common use is to select the 32-bit architecture on a 64-bit processor,
even if a 64-bit architecture is available.
.Pp
The
.Fl h
option prints a usage message and exits.
.Pp
The
.Ar arch_name
argument must be one of the currently supported architectures:
.Bl -tag -width x86_64 -offset indent
.It i386
32-bit intel
.It ppc
32-bit powerpc
.It ppc64
64-bit powerpc
.It x86_64
64-bit intel
.El
.Pp
Either prefix the architecture with a hyphen, or (for compatibility with
other commands), use
.Fl arch
followed by the architecture.
.Pp
If more than one architecture is specified, the operating system will try each
one in order, skipping an architecture that is not supported on the current
processor, or is unavailable in the universal binary.
.Pp
The
.Ar prog
argument is the command to run, followed by any arguments to pass to the
command.
It can be a full or partial path, while a lone name will be lookup in the user's
command search path.
.Pp
If no architectures are specified on the command line, the
.Nm arch
command takes the basename of the
.Ar prog
argument and searches for the first property list file with that basename and
the
.Pa \&.plist
suffix, in the
.Pa archSettings
sub-directory in each of the standard domains, in the following order:
.Bl -tag -width ".Pa /Network/Library/archSettings" -offset indent
.It ~/Library/archSettings
User settings
.It /Library/archSettings
Local settings
.It /Network/Library/archSettings
Network settings
.It /System/Library/archSettings
System settings
.El
.Pp
This property list contains the architecture order preferences, as well
as the full path to the real executable.
For examples of the property list format, look at the files in
.Pa /System/Library/archSettings .
.Ss Example
On an intel processor:
.Bd -literal -offset indent
% perl -MConfig -e 'printf "%s\\n", $Config{byteorder}'
1234
.Ed
.Pp
shows the intel little endian byte order, while:
.Bd -literal -offset indent
% arch -ppc perl -MConfig -e 'printf "%s\\n", $Config{byteorder}'
4321
.Ed
.Pp
runs the powerpc architecture, and displays big endian byte order.
.Ss Making links to the arch command
When a link is made to
.Nm arch
command with a different name, that name is used to find
the corresponding property list file.
Thus, other commands can be wrapped so that they have custom architecture
selection order.
.Pp
Because of some internal logic in the code, hard links to the
.Nm arch
command may not work quite right.
It is best to avoid using hard links, and only use symbolic links to the
.Nm arch
command.
.Ss Environment
The environment variable
.Ev ARCHPREFERENCE
can be used to provide architecture order preferences.
It is checked before looking for the corresponding property list file.
.Pp
The value of the environment variable
.Ev ARCHPREFERENCE
is composed of one or more specifiers, separated by semicolons.
A specifier is made up of one, two or three fields, separated by colons.
Architectures specified in order, are separated by commas and make up the last
(mandatory) field.
The first field, if specified, is a name of a program, which selects this
specifier if that name matches the program name in question.
If the name field is empty or there is no name field, the specifier matches
any program name.
Thus, ordering of specifiers is important, and the one with no name should
be last.
.Pp
When the
.Nm arch
command is called directly, the
.Ar prog
name provides the path information to the executable (possibly via the command
search path).
When a name is specified in a
.Ev ARCHPREFERENCE
specifier, the path information can alternately be specified as a second
field following the name.
When the
.Nm arch
command is called indirectly via a link, this path information must be
specified.
If not specified as a second field in a specifier, the executable path will
be looked up in the corresponding property list file.
.Ss Example ARCHPREFERENCE Values
.Bl -tag -width " "
.It ppc,i386,ppc64,x86_64
A specifier that matches any name.
.It foo:ppc,i386,ppc64,x86_64
A specifier that matches the program named
.Nm foo
(the full executable path is in the
.Pa foo.plist
file).
.It foo:/op/bin/boo:ppc,i386,ppc64,x86_64
A specifier with all fields specified.
.It baz:ppc,i386;i386,ppc
A specifier for
.Nm baz
and a second specifier that would match any other name.
.El
.Sh BUGS
Running the
.Nm arch
command on an interpreter script may not work if the interpreter is a link
to the arch command, especially if a 64-bit architecture is specified (since the
.Nm arch
command is 2-way universal, 32-bit only).
.Sh SEE ALSO
.Xr machine 1